Historically, lithographic web offset heat set inks contain between 30% and 45% volatile organic compounds (VOC). Besides being detrimental to the environment, VOCs are also flammable and hazardous to the printers who operate the press. Thus, it is desirable to reduce the VOC content in lithographic web offset heat set inks as much as possible. Initial attempts at solving this problem involved the use of chemical reactions that were triggered in a press oven. However, such oven cured ink systems did not have shelf stability.
Therefore, a heat setting web offset ink will typically contain the following major components (a) a high molecular weight ink resin to disperse the pigment and also to provide the toughness and gloss the ink requires on drying, (b) solvents to provide the fluidity to the ink before it is placed on the web and dried in an oven, (c) pigment, and (d) other minor components such as gellants, which provide structure to the ink, plasticizers (non volatile solvents), waxes, thickeners, and antioxidants. Conventional heatset inks set or dry by evaporation of the ink oil on heating at 250 to 300° F., and, to some degree, by penetration of the ink oil into the paper, leaving behind a hard polymeric film.
EP 731150 and EP 960911 describes rapid thermosetting low VOC web offset lithographic ink systems comprising solid resin, drying oil alkyds, bodied drying oil, vegetable oil, fatty acids, multifunctional unsaturated polyester, reducing agents and transition metal salts of organic acids and may also include an aqueous fountain solution containing peroxides that promote free radical polymerization of the ink.
WO 96/34922, U.S. Pat. No. 5,431,721, and U.S. Pat. No. 5,545,741, 1996 respectively describe lithographic inks which employ non-volatile solvents, but they set by penetration of the non-volatile solvent into the stock.
U.S. Pat. No. 7,018,453 describes a low VOC web offset heat set inks that contain a latex polymer. Due to its inherent incompatibility the gloss of printed film is dramatically reduced and at high speed piling occurs.
WO 2005/113694 describes an emulsion composition comprising water, a hydrocarbon distillate having a boiling point of 215 to 235° C., and a surfactant having a hydrophilic lipophilic balance number of 10 or less. However, the surfactant described in WO 2005/113694 is monomeric and the stability of the emulsified composition is not very good.
U.S. Pat. No. 5,417,749 describes a printing ink useful for “waterless” printing processes comprising a water-in-oil microemulsion wherein the water is present in an amount of about 5 to 20 wt. %, based on the weight of the ink. The water phase contains about 0.5 to 3 wt. %, based on the weight of the ink, of a water soluble surfactant which will not lower the surface tension (as measured at ambient temperature) of the ink.
In summary, traditional offset inks have high Volatile Organic Content (VOC) levels. The addition of water to the ink during manufacturing is one way to reduce the VOC level. However, prior attempts to emulsify water and reduce VOC content has been hampered by poor stability of the emulsified ink. Accordingly, there is a desire to develop better technology to stabilize pre-emulsified water in low VOC web offset heat set and offset inks that have good shelf stability and high dry speed.